Magnesium hydroxide sized photosensitive paper



MAGNESIUM nrnnoxnon srzn'n PriorosENsrrivE PAPER Hugo H. Hanson, Wynneswoozi, Pa, assignor to W.'C.'

Hamilton & Sons, Miquon, Pa., a corporation of Pennsylvania N Drawing. Application February 1, 1955 Serial No. 485,623 .7

7 Claims. (Cl. 96-75) This invention relates generally to the manufacture of blueprint paper and more particularly to improvements in the composition thereof and in the method of producing the same.

Heretofore and prior to the present invention, considerableattention has been devoted to the problem of producing a blueprint paper which, when developed, afforded maximum contrast between the blue background and the white lines of the developed print. The usual practice in the. art has been to coat the base paper with a light produce a negative wherein the design, of the original drawing showed up white against a blue 'blackground.

Various attempts have been made to increase the intensity of the blue background of the print, as by improving the composition of the paper base and/or the light sensitive coating, as well as the method of applying said coating. paper base prior to application of the light sensitive coating in order to impart to the fibers of the paper surface an increased capacity to absorb and retain the light sensitive solution which is later applied .to the paper. This precoating treatment is necessarily applied to the base paper by coaters who specialize in such processing of the paper base and, of course, adds materially to the cost of the blueprint paper so processed. I

I have'found that blueprint paper produced in accordance with my present invention, when coated with a suitable light-sensitizing solution, produces prints having a background of a uniformly intense pure blue color against which the design of the originaldrawing is'sharply de lineated in white, the contrast between the deep blue background and the white lines of the developed print being exceedingly sharp. Because of the fact that the improved blueprint paper of the present invention provides a print wherein the blue color of its background is of materially increased intensity, the printing time required for producing a satisfactory print of a given drawing may be reduced considerably.

In the preparation of the blueprint paper of the present invention, the paper stock in the form of a conventional suspension or slurry of finely divided rag and/or wood It has been proposed also to precoat the pulp having incorporated therein a suitable internal sizing of rosin and aluminum sulphate is conventionally fed over a wire screen conveyor from which it emerges as a paper web of continuous length, this web being then passed successively through suitable pressing rolls and drying cylinders to a surface sizing station wherein the dried web of paper is surface coated with the sizing solution of the present invention. Thereafter, also in accordance with conventional paper making procedure, the surface-sized paper is calendered and then wound into rolls of any desired size, in which form the paper is supplied to the ice blueprint coaters in condition ready to be surface coated with the requisite light-sensitizing solution. l v

The solution for surface-sizing the paper in accordance with the present invention includes as its principal ingredient finely precipitated magnesium hydroxide, which, when deposited out of the sizing solution onto the surface of the paper, not only so increases the area thereof that a greater thannormal amount of the light sensitizing solution may be applied to the paper, but also increases the wetability of the paper surface for its better absorption and retention of the light sensitizing coating.

Photomicrographic studies of ordinary blueprint'paper base coated with light sensitizing solution indicate that this coating solution stains the paper base only to a depth of approximately one fiber diameter, in consequence of which the coating is apt to appear speckled under the microscope.

From photomicrographic study and analysis of the blueprint pap-er processed in accordance with the present invention it was noted that in such paper, when surface coated. with the light sensitive solution and then exposed to light and developed pursuant to conventional blueprinting procedure, the blue pigment of the finished print, consisting primarily of Prussian blue, penetrated the paper to a depth of at least two fiber diameters and that all of the fibers at the coated surface of the paper were uniformly stained blue throughout their cross-sectional areas, thus indicating exceedingly good'penetration an retention of the light sensitive solution in the paper sur face. It was noted also that in the paper processed in accordance with the present invention, the after-applied light sensitive coating was much more uniformly 'distributed throughout the paper surface, so much so, that upon exposure and development of the paper, there was obtained a much more even dispersion and deposition of the blue pigment about and between the fibers of the paper immediately adjacent the surface thereof, resulting in a blue background which was free of any appreciable speckling such as causes the appearance of an objectionable slatish blue color. 7 I p i The surface sizing solution of the present invention is prepared in accordance with the following preferred formula:

Water gall0ns 500 Magnesium hydroxide pounds 120 Glue don Formaldehyde (20% concentration) gallons 1 The magnesium hydroxide employed in the sizing solu tion is of microscopic particle size and in all materini respects, is the same as that conventionally prepared fo medicinal purposes, e. g., as an antacid in milk of magnesia, while the glue of the composition may be any form of animal, vegetable or other glue of good quality, preferably such as is manufactured from proteinaceous material of animal or vegetable origin. In the above formula the magnesium hydroxide represents about 2.7 percent of the weight of the solution, but it will be understood that this percentage may vary within a range of from 1 to 7 percent. Also, the proportions of the glue and of the formaldehyde as respectively set forth in the above example may vary plus or minus 10 percent.

In certain cases it may be desirable to employ hydrated magnesium hydroxide in the form of a paste, in which event a sufficient amount of the paste would be used to include the magnesium hydroxide in a solution in an amount ranging from 1 to 7 percent by weight of the solution.

The magnesium hydroxide, which is diflicultly soluble, is present in the solution as a water dispersion, in which form it is maintained by the glue content of the solution. On passing the paper web through this surface sizing solution, there is deposited on the paper a surface layer of discrete microscopic particles of the magnesium hydroxide. The magnesium hydroxide particles are permanently fixed to the surface by the glue contents of the solution, the glue itself being tanned or hardened by the formal dehyde to better condition the paper surface against being adversely affected by the wet processing treatments to which it is subsequently subjected, e. g., the application of the light sensitizing solution and the conventional blueprinting steps. H 1

In lieu of employing formaldehyde to tan or harden the glue in the composition of the formula above set forth,jthere may beflemployedimelamine, urea formal dehyde, hexamethylene tetramirle 'or aluminum sulphate. It will be understood,ialso, that any other suitable binding agentmay be employed for fixing the deposited particles of magnesium'hydroxide upon the surface of the paper, asfor example, suitable vegetable'starches or or ganic derivatives of cellulose,such as -carboxy-meth'yl cellulose and carboxy-ethyl cellulose. In any event,'fthe binding agent, whether it be one consisting of glue combined with a hardening agent, e. g., formaldehyde, or any of its above mentioned sublstitutes,or one which does not include glue as a constituent, e. g., vegetablestarch, car boxy-methyl cellulose, or carboxy-ethyl cellulose, ispres ent in the composition in an amount sufiicient repermanently fix on the sized surface of the paper a layer of that the surface sizing solution of the present invention uniformly distributed microscopic particlesof magnesium hydroxide. As indicated by the above formula, thebinding agent is present in the composition in an amount which preferably, approximates 50 to 75 percent of the weight of the magnesium hydroxide in a water dispersion thereof.

It is believed that the improved background color, contrast of the white lines with the background color and speed of printing of the blueprint paper prepared fin accordance 'with the present invention result not only from the fact that the layer of microscopic particles of magnesium hydroxide on the surface of the paper increases the area, depth and concentration of the light sensitizing coating subsequently applied to the-paper, but also from the'fact that the magnesium hydroxide sizing solution is of a pH of from 8.5 to 10 and thus is of an alkalinity sufficiently high to weaken the internal sizing slightly and insure penetration of the light sensitizing solution into the surface of the paper for a depth of at least 2 fiber diameters, in consequence of which the light sensitizing solution at the surface of the paper is in substantially con tinuous phase.

Inasmuch as magnesium hydroxide is quite stable at the normal operating temperature of the surface sizing solution, which temperature is from 125 to 140 F., as determined by the heat of the paper delivered from the drying rolls to the surface sizing bath, it will be apparent may be advantageously applied to the paper by the ordinary tub sizing procedure such as is now conventionally used in paper making mills for the preparation of blueprint paper.

It will be understood, of course, that the present invention is susceptible of various changes and modifications which maybe made from time to time without departing from the general principles or real spirit thereof, and it is accordingly intended to claim the same broadly, as well as specifically, as indicated by the appended claims.

What is claimed as new and useful is:

1. A photosensitive paper comprising a paper base having thereon a surface sizing of magnesium hydroxide and an agent for fixing the magnesium hydroxide upon the paper surface, anda light sensitive coating on said sized paper base of light sensitive salts.

2. A photosensitive paper as wherein said agent is glue.

3. A photosensitive paper as set forthin claim 1, wherein said agent is the reaction product of a 'glue 'derived tromproteinaceous material and formaldehyde.

4. A photosensitive paper as set forth in claim 1, wherein said'agent is glue combined with a glue hardening agent selected from the group consisting of formal dehyde, urea formaldehyde, melamine, aluminum sulfate, and hexamethylene tetramine.

5. A photosensitive paper as set forth in claim 1, wherein said agent is a vegetable starch.

6. A photosensitive paper as set forth in claim 1, wherein said agent is an organic derivative of cellulose.

7. A photosensitive blueprint paper comprising a paper base having thereon a surface sizing of magnesium hydroxide and an agent for fixing the magnesium hydroxide upon the paper surface, and a light sensitive blueprint coating on said sized paper base precipitated from an iron salt solution.

set forth in claim 1,

References Cited in the file of this patent UNITED STATES PATENTS 51,010 Brinckerhoff Nov. 21, 1865 61,338 Hover Jan. 22, 1867 1,934,639 Rafton Nov. 7, 1933 1,935,434 Cohen Nov. 14, 1933 2,608,546 Jackson Aug. 26, 1952 2,626,867 Webster Ian. 27, 1953 2,639,989 Conover May 26, 1953 2,705,685 Cpriano Apr. 5, 1955 OTHER REFERENCES I Institute of Paper Chemistry, Clarence J. West, Bibliographic Series, Number 165. Copyright 1945, Sizing of Paper. 

7. A PHOTOSENSITIVE BLUEPRINT PAPER COMPRISING A PAPER BASE HAVING THEREON A SURFACE SIZING OF MAGNESIUM HYDROXIDE AND AN AGENT FOR FIXING THE MAGNESIUM HYDROXIDE UPON THE PAPER SURFACE, AND A LIGHT SENSITIVE BLUEPRINT COATING ON SAID SIZED PAPER BASE PRECIPIUTATED FROM AN IRON SALT SOLUTION. 